93 - Stationary Points - Critical Points Revisited
Critical Points in single variable calculus are the points we're used to where the first derivative is zero, and the same is the case for multivariable calculus, except that instead of the derivative we have the gradint zero.
Such points are called stationary points.
We have functions of multiple variables involved. In many cases, after a stationary point, two variables may disagree on the sign, for example one goes up the other down. This forms a saddle pattern on the graph, and because of this such cases are promptly called saddle points, which is another scenario possible in addition to the usual maxima and minima.